Trench capacitors are widely used in Dynamic Random Access Memory (DRAM) devices for data storage. A trench DRAM cell consists of a trench capacitor and a transistor. The trench capacitor typically consists of a hole etched into the substrate, a first electrode—often referred as a “buried plate”—in the substrate, a second electrode in the trench, and a thin storage-node dielectric which separates those two electrodes. The transistor is formed above the trench capacitor.
Deep trench capacitors can also be used as decoupling capacitors which can stabilize the voltage level across the chip and significantly improve chip performance. The buried plates of deep trenches used for different purposes may require different biases to operate, thus, different buried plate regions need to be isolated from each other.
A buried plate is formed in the substrate adjacent the trench by out-diffusing a dopant such as arsenic (As) into the substrate. Buried plate doping may be formed by conventional solid phase doping processes such as out-diffusing arsenic from a layer of arsenic-doped silicon glass (ASG) on trench sidewall, liquid phase doping, gas phase doping (GPD), plasma doping, plasma immersion ion implantation, infusion doping, or any combination of these methods that are well known in prior art.
However, as consumers are demanding products with more processing power, and smaller physical size, there is a need to improve the performance of various integrated circuits, such as DRAM devices. This is driving a trend towards smaller and smaller dimensions. As the trend towards miniaturization continues, the aforementioned prior art method for forming the buried plate have drawbacks, such as being limited by the aspect ratio (AR) of the trench, and requiring a sidewall spacer. Therefore, it is needed to have an improved method for fabricating a trench capacitor that is suitable for smaller technologies, which provides the high performance and small size demanded by today's electronic devices.